The present invention relates to a driving apparatus for a MOS (metal oxide-semiconductor) transistor and, more particularly, to a driving apparatus for a MOS power transistor which controls an amount of a large current supplied to a winding with a large inductance.
For example, current is supplied to a field winding of a generator for an automobile, and an amount of the current is controlled by a MOS power transistor. At the time of controlling an amount of current supplied to a field winding of a generator for an automobile, there arises a problem that radio noise is generated.
As an example of an apparatus having means for suppressing the generation of such radio noise, there is a voltage regulator disclosed in JP-A-64-20000. In the voltage regulator disclosed in JP-A-64-20000, in order to decrease the radio noise, a current flowing into a field winding is controlled in a manner that a value of a current flowing into the field winding at the time of switching is subjected to feedback control so that an amount of change in the field current is not more than a constant value.
However, since the voltage regulator disclosed in JP-A-64-20000 performs the feedback control as to a value of a current flowing into the field winding, the voltage regulator requires expensive parts such as a current detection circuit for detecting a field current, an operational amplifier etc. Accordingly, the voltage regulator has a problem that the arrangement thereof is complicated and a cost thereof is expensive.
Accordingly, an object of the present invention is to provide a driving apparatus for a MOS transistor which is able to suppress the generation of radio noise etc. with a simple configuration and cheep cost.
In order to attain the aforesaid object, according to an aspect of the present invention, there is provided with a driving apparatus for a MOS transistor which includes a diode connected in parallel to a winding which is connected in series with a battery; a MOS transistor connected between the winding and the battery; a driving circuit which generates signals for turning on and off the MOS transistor to drive a gate of the MOS transistor; and a delay circuit which is disposed between the driving circuit and the MOS transistor and delays the signal generated from the driving circuit for changing the MOS transistor from a turned-off state to a turned-on state so that the MOS transistor is shifted from a completely turned-off state to a completely turned-on state with a predetermined time period longer than a reverse recovery time of the diode.
The delay circuit serves to shift the MOS transistor from the completely turned-off state to the completely turned-on state with the time period longer than the reverse recovery time of the diode. Accordingly, there flows little reverse current through the diode and so such a phenomenon is prevented from occurring that the short-circuit current flows through the battery, the diode and the MOS transistor.
In this case, the delay circuit can be formed by a simple circuit including transistors, a capacitor etc.
According to another aspect of the present invention, there is provided with a driving apparatus for a MOS transistor which includes a diode connected in parallel to a winding which is connected in series with a battery; a MOS transistor connected between the winding and the battery; a driving circuit which generates signals for turning on and off the MOS transistor to drive a gate of the MOS transistor; and a function generation circuit which is disposed between the driving circuit and the MOS transistor and converts the signal generated from the driving circuit for changing the MOS transistor from a turned-off state to a turned-on state into a voltage-which is to be applied to the gate of the MOS transistor as a voltage of time function gradually increasing with time lapse so that the MOS transistor is shifted from a completely turned-off state to a completely turned-on state with a predetermined time period longer than a reverse recovery time of the diode.
The function generation circuit applies the voltage of time function gradually increasing with time lapse to the MOS transistor thereby to shift the MOS transistor from the completely turned-off state to the completely turned-on state with the time period longer than the reverse recovery time of the diode. Accordingly, there flows little reverse current through the diode and so such a phenomenon is prevented from occurring that the short-circuit current flows through the battery, the diode and the MOS transistor.
In this case, the function generation circuit can be formed by a simple circuit including transistors, a capacitor etc.
According to still another aspect of the present invention, there is provided with a driving apparatus for a MOS transistor which includes an armature winding of a generator for charging a battery; a diode connected in series with the battery and connected in parallel to a filed winding for supplying magnetic flux to the armature winding; a MOS transistor connected between the field winding and the battery; a driving circuit which generates signals for turning on and off the MOS transistor to drive a gate of the MOS transistor; and a delay circuit which is disposed between the driving circuit and the MOS transistor and delays the signal generated from the driving circuit for changing the MOS transistor from a turned-off state to a turned-on state so that the MOS transistor is shifted from a completely turned-off state to a completely turned-on state with a predetermined time period longer than a reverse recovery time of the diode.
According to still another aspect of the present invention, there is provided with driving apparatus for a MOS transistor which includes an armature winding of a generator for charging a battery; a diode connected in series with the battery and connected in parallel to a filed winding for supplying magnetic flux to the armature winding; a MOS transistor connected between the field winding and the battery; a driving circuit which generates signals for turning on and off the MOS transistor to drive a gate of the MOS transistor; and a function generation circuit which is disposed between the driving circuit and the MOS transistor and converts the signal generated from the driving circuit for changing the MOS transistor from a turned-off state to a turned-on state into a voltage which is to be applied to the gate of the MOS transistor as a voltage of time function gradually increasing with time lapse so that the MOS transistor is shifted from a completely turned-off state to a completely turned-on state with a predetermined time period longer than a reverse recovery time of the diode.
Preferably, the function generation circuit includes a capacitor, a charge/discharge circuit for charging and discharging the capacitor in synchronism with the signals for turning on and off the MOS transistor, and an amplifier for outputting a voltage corresponding to a voltage of the capacitor.